Field of the Invention
The present invention relates to a fuel cell including a membrane electrode assembly and separators provided on both surfaces of the membrane electrode assembly. The membrane electrode assembly includes a first electrode, a second electrode, and a solid polymer electrolyte membrane interposed between the first electrode and the second electrode. Each of the first electrode and the second electrode includes an electrode catalyst layer and a gas diffusion layer.
Description of the Related Art
In general, a solid polymer electrolyte fuel cell employs a solid polymer electrolyte membrane. The solid polymer electrolyte membrane is a polymer ion exchange membrane. In the fuel cell, the solid polymer electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). Each of the anode and the cathode includes a catalyst layer (electrode catalyst layer) and a gas diffusion layer (porous carbon). The membrane electrode assembly is sandwiched between separators. In use, generally, a predetermined number of fuel cells are stacked together to form a fuel cell stack, e.g., mounted in a vehicle.
In some cases, in the membrane electrode assembly of this type, the position of an outer end of one catalyst layer and the position of an outer end of the other catalyst layer are offset from each other in the membrane thickness direction of the solid polymer electrolyte membrane.
For example, as shown in FIG. 17, a membrane electrode assembly disclosed in Japanese Laid-Open Patent Publication No. 2006-338938 (hereinafter referred to as the conventional technique 1) includes a polymer electrolyte membrane 1a, a cathode catalyst layer 2a provided on one surface of the polymer electrolyte membrane 1a, an anode catalyst layer 3a provided on the other surface of the polymer electrolyte membrane 1a, and a first gasket layer 4a formed on at least part of an end of the cathode catalyst layer 2a such that the effective surface area of the anode catalyst layer 3a is larger than the effective surface area of the cathode catalyst layer 2a. 
Further, a reinforcement layer 5a is provided at a portion where the polymer electrolyte membrane 1a and the end of the cathode catalyst layer 2a are overlapped with each other at least in the thickness direction of the membrane electrode assembly. The reinforcement layer 5a is harder than the polymer electrolyte membrane 1a. 
Further, as shown in FIG. 18, for example, a solid polymer electrolyte fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2008-135295 (hereinafter referred to as the conventional technique 2) is formed by combining gas diffusion layer elements 1b on both sides of the membrane electrode assembly 2b. The membrane electrode assembly 2b includes a polymer electrolyte membrane 3b, and catalyst layers 4b are formed on both surfaces of the polymer electrolyte membrane 3b. 
The gas diffusion layer element 1b includes a sheet like porous base member 5b, e.g., made of carbon material having gas-permeable and electrically-conductive property, and sealing resin 6b, e.g., made of thermoplastic resin such as polycarbonate based resin. Pores in an outer end of the porous base member 5b are impregnated with the sealing resin 6b. Impregnation of the sealing resin 6b is performed by irradiating, with a laser beam, a sealing resin film stacked on the outer end to melt the sealing resin film, whereby a seal area 7b is formed.